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[[file:Coal_Bituminous.jpg|thumb|300px|Coal. [http://geosurvey.state.co.us/energy/Coal/Pages/Whatisit.aspx Courtesy Colorado Geological Survey].]]

[[file:Coal_Bituminous.jpg|thumb|300px|Coal. [http://geosurvey.state.co.us/energy/Coal/Pages/Whatisit.aspx Courtesy Colorado Geological Survey].]]

Coal is a rock that contains greater than 50 wt. % organic matter. Most coals in North America and Europe originate mainly from higher plants and consist of type III (gas-prone) [[kerogen]] dominated by [[Thermal maturation#Vitrinite|vitrinite]] group [[maceral]]s. Thermal maturation transforms peat to lignite, bituminous coal, and then anthracite coal.<ref name=Petersetal_2012>Peters, Kenneth E., David J. Curry, and Marek Kacewicz, 2012, [http://archives.datapages.com/data/specpubs/hedberg4/INTRODUCTION/INTRODUCTION.HTM An overview of basin and petroleum system modeling: Definitions and concepts], ''in'' Peters, Kenneth E., David J. Curry, and Marek Kacewicz, eds., Basin modeling: New horizons in research and applications: [http://store.aapg.org/detail.aspx?id=1106 AAPG Hedberg Series no. 4], p. 1-16.</ref>

Coal is a rock that contains greater than 50 wt. % organic matter. Most coals in North America and Europe originate mainly from higher plants and consist of type III (gas-prone) [[kerogen]] dominated by [[Thermal maturation#Vitrinite|vitrinite]] group [[maceral]]s. Thermal [[maturation]] transforms peat to lignite, bituminous coal, and then anthracite coal.<ref name=Petersetal_2012>Peters, Kenneth E., David J. Curry, and Marek Kacewicz, 2012, [http://archives.datapages.com/data/specpubs/hedberg4/INTRODUCTION/INTRODUCTION.HTM An overview of basin and petroleum system modeling: Definitions and concepts], ''in'' Peters, Kenneth E., David J. Curry, and Marek Kacewicz, eds., Basin modeling: New horizons in research and applications: [http://store.aapg.org/detail.aspx?id=1106 AAPG Hedberg Series no. 4], p. 1-16.</ref>

Although [[oil as an energy source|oil]] is, at present, the principal source of energy in the world (easier to produce, transport, store, and use) and [http://www.glossary.oilfield.slb.com/en/Terms/n/natural_gas.aspx gas] is acclaimed as the fuel of the future because it is the cleanest burning of the main sources of energy, coal is, by far, the most abundant and lowest cost [https://www.udemy.com/blog/types-of-fossil-fuels/ fossil fuel] source of energy; coal reserves are 5 times as large as either oil or gas reserves, and coal resources are estimated to be about 17 times the oil resources and 20 times the gas resources.

Although [[oil as an energy source|oil]] is, at present, the principal source of energy in the world (easier to produce, transport, store, and use) and [http://www.glossary.oilfield.slb.com/en/Terms/n/natural_gas.aspx gas] is acclaimed as the fuel of the future because it is the cleanest burning of the main sources of energy, coal is, by far, the most abundant and lowest cost [https://www.udemy.com/blog/types-of-fossil-fuels/ fossil fuel] source of energy; coal reserves are 5 times as large as either oil or gas reserves, and coal resources are estimated to be about 17 times the oil resources and 20 times the gas resources.